Dr. Haighton's experimental Inquiry , &c. 191 
sal; and this power of repairing in kind has been denied to 
several of the constituent parts of an animal machine. With 
respect to the nerves, it has been both affirmed and denied : 
some assert, that the new formed substance possesses the cha- 
racters of the primitive nerve; others maintain, that it is 
totally different; and both found their opinions on experi- 
ment. 
When opinions so opposite to each other prevail on a point, 
which experiment seems so fully adequate to decide, we are na- 
turally led to take a view of the manner in which the experi- 
ments were conducted, and consider the criterion to which each 
party appealed.* 
There are only two tests which seem to offer themselves, 
and from which any degree of judgment can he formed. These 
are, either a minute and careful examination of the new formed 
substance in an anatomical way, and an accurate comparison 
of it with the original nerve ; or, a cautious attention to the 
function of that nerve, by which we see the loss of it from the 
division, and the return of it from the reunion of the divided 
parts. 
Those who have subjected this matter to the test of experi- 
ment, have made their appeal tq the first criterion ; and have 
either affirmed or denied the reproduction, according as they 
thought the new formed part either agreed with or differed 
from the original nerve. 
This criterion certainly supposes, that anatomy is fully com- 
petent to determine, what is the precise structure of nerves, 
what are the nature and characters of ultimate nervous fibres, 
and by what mechanism or power they execute their allotted 
* Vide Fontana, and Arnemann. 
